The present invention relates to medical devices in general, and in particular to atherectomy devices for removing occluding material from a patient""s blood vessels.
Arteriosclerosis is a common vascular disease in which a patient""s blood vessels become hardened and blocked by plaque or clots that impede blood flow. Left untreated, this condition is a major contributing factor to the occurrence of high blood pressure, strokes and cardiac arrest.
To treat arteriosclerosis, many invasive and non-invasive techniques have been developed. For example, cardiac bypass surgery is now a commonly performed procedure whereby an occluded cardiac artery is bypassed with a segment of a healthy blood vessel that is obtained from elsewhere in the body. While this procedure is generally successful, it is fairly traumatic because the entire chest cavity must be opened to access the occluded vessel. Therefore, the procedure is not generally performed on elderly or relatively frail patients.
One example of a promising minimally invasive technique that can be performed on a greater number of patients is to remove the occluding material from a patient""s vessel in an atherectomy procedure. To perform this procedure, a guide catheter is typically inserted into the patient""s femoral artery and advanced until the distal end of the guide catheter is located in the patient""s coronary ostium. A guide wire is then inserted through the guide catheter and traversed into the coronary arteries and past the occluded material to be treated. Then, as described in U.S. Pat. No. 4,990,134, issued to Auth, an atherectomy catheter having a small abrasive burr is advanced through the guide catheter and over the guide wire to the point of the occlusion. The burr is then rotated at high speed and passed through the occlusion to remove particles that are sufficiently small such that they will not occlude in the distal vasculature. As the burr removes the occlusion, a larger lumen is created in the vessel and blood flow is restored.
It is well recognized that the risk of certain patient complications increases with the size of the guide catheter through which minimally invasive devices are routed. Larger guide catheters require larger access holes in the femoral artery, creating the potential for patient complications, such as the sealing of the puncture site after completion of the procedure. Therefore, physicians generally wish to utilize the smallest possible guide catheter during a procedure. However, the smaller size guide catheters can only accommodate corresponding smaller size ablation burrs. Therefore, if a large vessel is to be treated, a larger burr and corresponding larger guide catheter must be used to successfully remove all of the occlusion from the patient""s vessel.
In addition, it has also been discovered that when performing an atherectomy procedure as described earlier, it has been beneficial to remove only a small amount of the occlusion at a time. Therefore, currently many procedures are performed using multiple passes through the occlusion with different sized ablation burrs. While these procedures have proven effective, the use of multiple devices for a single procedure adds both time and cost to the procedure.
Given the disadvantages of the existing atherectomy devices, there is a need for an atherectomy device that can treat different size vessels while being traversed through a small guide catheter.
To eliminate the need for a physician to utilize larger guide catheters in order to route a larger diameter ablation burr in a patient, the present invention comprises an expandable ablation burr. The ablated diameter preferably has a diameter that exceeds the diameter of a guide catheter through which the burr is routed.
According to one embodiment of the invention, the ablation burr includes a polymeric balloon that expands as the burr is rotated. A portion of the balloon is coated with an abrasive such that the balloon will ablate an occlusion as the burr is rotated and advanced through a vessel.
According to another aspect of the present invention, the expandable ablation burr includes an expansion control mechanism which allows the ultimate or final outer diameter of the burr to be predetermined and controlled to create a new lumen in the patient""s vessel. The burr includes a nose and end section with an elastic tube section coupled in-between. The burr is expanded due to centrifugal force. A portion of the tube section is coated with an abrasive such that the tube section will ablate an occlusion as the burr is rotated and advanced through a vessel.
In one embodiment, the expansion control mechanism includes reinforcement fibers embedded into the elastic tube section. The reinforcement fibers prevent the tube section from over-expanding when rotated. A portion of the tube section is coated with an abrasive such that the expanded tube section will ablate an occlusion as the burr is rotated and advanced through a vessel.
In another embodiment, the tube includes inner and outer layers with the expansion control mechanism containing a layer of ePTFE disposed in-between the inner and outer cast film layers. The ePTFE layer prevents the ablation burr from over-expanding.
In another embodiment, the expansion control mechanism includes post cross-linking of the tube section. The post cross-links prevent the ablation burr from over-expanding.
In yet another embodiment, the expansion control mechanism includes curvilinear ribs on the interior of the tube section. The curvilinear ribs prevent the ablation burr from over-expanding.
In yet another embodiment, the expansion control mechanism includes alternating braided layers of a non-elastic polymeric material in-between the inner and outer layers of the tube section. The alternating braided layers prevents the ablation burr from over-expanding.
According to another aspect of the present invention, a reverse pull-back ablation burr system includes an ablation burr having an abrasive disposed on its proximal end for ablating an occlusion when the burr is pulled back through the occlusion toward the guide catheter. The systems further include an aspiration catheter that aspirates the loose gromous that is ablated by the ablation burr.
In one embodiment, the system prevents the loose gromous of a Saphenous Vein Graft from reembolizing by using the ablation burr in its expanded state as a seal. The burr is pulled back in a reverse fashion to ablate the lesion. Similarly, a distal balloon or filter could be deployed to prevent accident embolization.
In another embodiment, the system prevents the loose gromous from reembolizing by including a self expanding seal coupled to the aspiration catheter. The seal is deployed after the ablation burr is routed through the lesion. As the burr is pulled back in a reverse fashion to ablate the lesion, a vacuum is applied to the aspiration catheter to remove the loose gromous from the vasculature.